Description:
------------
If you set a session variable with the root key as a numeric 
string it fails to save. It also fails to save anything else 
in the array after the numeric rook key string.

This was via FCGI with lighttpd, but also reproduced on Debian 
etch with apache2.

Reproduce code:
---------------
Set a session :-

<?php
session_start();

$_SESSION['Test1'] = "This should be ok";
$_SESSION['123']['test']="This is a test";
$_SESSION['Test2'] = "This is not saved";
?>
<PRE>
Session Set:
<?php print_r($_SESSION); ?>
</PRE>

Read it :-

<?php
session_start();

?>
<PRE>
Session Read:
<?php print_r($_SESSION); ?>
</PRE>

Expected result:
----------------
I would expect to see the same details in the session from the 
second piece of code as output from the first. :-

Session Read:
Array
(
    [Test1] => This should be ok
    [123] => Array
        (
            [test] => This is a test
        )

    [Test2] => This is not saved
)

Actual result:
--------------
Session Read:
Array
(
    [Test1] => This should be ok
)